1. Field of the Invention
The present invention generally relates to a signal adjusting circuit, and more particularly, to a signal adjusting circuit capable of adjusting different signals.
2. Description of Related Art
Recently, digital television has been more and more popularly used. Briefly, digital television is a new broadcasting technology, for broadcasting analog signals transmitted from television stations in a digital manner. Comparing with conventional television, digital television has the advantages such as multichannel, interaction, mobile receiving, and a synchronization.
FIG. 1 is a block diagram illustrating a conventional video apparatus. Referring to FIG. 1, an analog-to-digital converter (ADC) 110 converts an analog video signal received thereby into a digital video signal. Then, the digital video signal is filtered by a low pass filter (LPF) 120, for removing high frequency component of the digital video signal. Then, the filtered digital video signal is transmitted via a multiplier 130 to a video decoder 140 and an auto-gain controller (AGC) 150, respectively. After being gained by the multiplier 130, the digital video signal is subsequently processed by the video decoder 140 for video signal processing. Further, when the AGC 150 received the filtered and gained digital video signal, it generates a corresponding gain value according to a status of the digital video signal. Then, when a clamp circuit 160 receives the gain value, the clamp circuit 160 restricts the gain value between an upper limit and a lower limit set by the clamp circuit 160, so as to generate an adjustment value and provide the adjustment value to the multiplier 130, for adjusting the digital video signal.
Typically, the digital video signal includes a synchronous signal S and an active video signal A. However, in the conventional video apparatus 100, the AGC 150 generates the corresponding gain value according to a comparison between an instant synchronous signal and a standard synchronous signal. Specifically, when the instant synchronous signal is smaller than the standard synchronous signal, the AGC 150 outputs a larger gain value, for allowing the instant synchronous signal outputted to the video decoder 140 to be equivalent with the standard synchronous signal, thus the video apparatus 100 can output a relatively correct image. Correspondingly, when gaining an instant synchronous signal S with a certain multiple, the active video signal A is gained with the same certain multiple by the way. However, the synchronous signal S and the active video signal A have different features, and the posterior stage circuit (including the video decoder 140) may demand for different upper limits and lower limits regarding these two components S and A. For example, when gaining the digital video signal for a y multiple (supposing that a y multiple gained synchronous signal S is positioned within its upper limit and lower limit), the y multiple gained active video signal A may unfortunately exceed an upper limit that can be processed by the posterior stage circuit. As such, the brightness of the image outputted by the video apparatus 100 will be increased, and the viewer may feel uncomfortable when viewing such an image. Or otherwise, a portion of the y multiple gained active video signal A exceeding the upper limit that can be processed by the posterior stage circuit is clamped as the upper limit. This may cause a distortion of the image.